A medical powder which comprises a polymeric microsphere obtained by a polymerization method, such as emulsion polymerization, soap-free emulsion polymerization, and having thereon an immobilized antigen or antibody, and which is used for diagnosis where its cohesiveness with an antigen or antibody as the substance to be detected is examined is conventionally known as an immunolatex. A technique of using a labeled antibody as the immobilized antibody in an immunolatex is used for heightening detectability in diagnosis. Also, a technique in which a drug is supported on an immnunolatex together with an antibody and this immunolatex is used for delivering the drug to, e.g., cancer cells having an antigen responsive to the supported antibody, is used.
Beads are more frequently used as drug carriers for drug delivery than latexes because they have the higher ability to support drugs. The term "beads" means polymeric microspheres having larger particle diameters than the latexes. Latexes have particle diameters in the range of about 100 .ANG. to about submicron sizes (1 .mu.m or less), while beads have particle diameters in the range of submicron sizes to several millimeters. The beads comprising a polymeric compound and having thereon an immobilized antigen or antibody are generally called immunobeads.
Beads comprising a polymeric compound which contain a drug embedded therein and have thereon an immobilized antibody are used for delivering the drug to a diseased part where a responsive antigen is present. Namely, these are a kind of drug delivery beads.
Although biodegradable natural polymeric compounds, i.e., gelatin, starch, fibrinogen, and the like, have been used as preferred bead materials for such drug delivery beads, they have drawbacks, for example, that particle diameter control is difficult, beads of constant quality are difficult to obtain, and storage is difficult. Consequently, use of synthetic or semisynthetic polymeric compounds is progressing.
The immobilization of an antigen or antibody on the latex particles or beads is accomplished, for example, by bonding the protein (constituent substance of the antigen or antibody) with a condensing agent, e.g., cyanogen bromide or carbodiimide, to a reactive group, e.g., a hydroxyl group, an amino group, or a carboxyl group, present on the main chain of the polymeric compound constituting the latex particles or beads or to such a reactive group incorporated as a side chain into the constituent polymeric compound through substitution.
Another known example of the fields where the immunobeads are utilized is the field of cell separation. An example of immunobead utilization in the field of cell separation is in therapy or diagnosis. In this application, magnetic immunobeads (hereinafter referred to also as "magnetosensitive immunobeads") are prepared by fixing a ferromagnetic substance to polymeric beads, for example, by incorporating an iron powder or another ferromagnetic material powder into the beads or embedding aggregates of ferromagnetic material powder particles in the beads and further immobilizing an antibody to the surface of the beads. The magnetosensitive immunobeads are introduced into the blood to allow the immunobeads to react with a responsive antigen (pathogenic antigen) present in the blood to thereby immobilize the antigen to the immunobeads. The magnetosensitive immunobeads are then collected with a magnet to thereby remove the antigen from the blood. The magnetosensitive immunobeads thus used for removing a pathogenic antigen from the blood are used also for removing tumor cells from bone marrow.
Still another use of magnetosensitive beads is in drug delivery. Specifically, magnetosensitive beads are used as a therapeutic powder in a drug delivery system in which the magnetosensitive beads are intravenously injected into a living body, e.g., human body, and a magnet or the like is externally applied to a diseased part to lead the drug-supporting magnetosensitive beads to the diseased part by means of magnetic induction. An example of these magnetosensitive beads is a medical powder comprising a polymeric microsphere which contains a magnetite as a base material embedded therein and simultaneously have a drug supported thereon.
Furthermore, a medical powder comprising a metallic conductor is used as a heating medium in the method of treatment called hyperthermia, in which a powder of a conductor such as a metal (a metal powder is generally used) is introduced into a part affected by terminal cancer and the affected part is burnt by high-frequency induction heating.
The current medical powder which comprise a polymeric microsphere containing a magnetite as a base material embedded therein and is used for the diagnostic-therapeutic system described above (i.e., one form of the magnetosensitive beads described above) employs a magnetite as a base material. However, since the magnetic force applied with current magnetic inductors is insufficient for these current medical powders, the locations of diseased parts to which the medical powders can be led are limited. There is hence a desire for a medical powder (i.e., magnetosensitive beads) having higher magnetic sensitivity.
Additionally, during long-term residence in a living body, the current magnetosensitive beads suffer changes such as, e.g., oxidation of the embedded base material and come to have reduced magnetic sensitivity. There have also been cases where ions such as iron ions are released from current magnetosensitive beads. Thus, the current magnetosensitive beads have the unsolved problems described above.
An object of the present invention is to eliminate the problems of the current magnetosensitive beads and to provide a safer medical powder which has excellent performances when used for the diagnosis, therapy, or drug delivery described above.